The South American tomato pinworm, T. absoluta (Lepidoptera—Gelechiidae also known as Scrobipalpula absoluta, Scrobipalpuloides absoluta, Gnorimoschema absoluta, and Phthorimaea absoluta) is one of the most severe pests for solanaceous plants, especially tomatoes. According to Maluf et al. (Euphytica, 2010, 176:113-123), T. absoluta is an insect of neotropical distribution considered as a major tomato pest in several Latin American countries, including Argentina, Chile, Peru, Bolivia, Ecuador, Colombia, Venezuela, Uruguay and Brazil. It was reported for the first time in Europe in 2006, in the Spanish province of Castellon, and has since been reported in other parts of Spain (Valencia, Ibiza, Almeria, Murcia and Catalunya) and of the Mediterranean basin, including tomato-producing areas of Morocco and Algeria, and more recently in Israel, Turkey, Syria, Germany, Hungary, Lithuania and Serbia.
T. absoluta attacks the plants in all of their developmental stages, damaging the leaf mesophyll, stems, stem apexes, flowers and fruits. According to Maluf et al., oviposition of T. absoluta is predominantly on leaflets (on both abaxial and adaxial surfaces) of the upper third of the plant, but can also occur in stems and flowers. Larvae feed predominantly on leaf parenchyma tissue, on tender portions of the stems (especially axillary buds), and in both developing and mature fruit. Leaf mining can evolve until all the parenchyma tissue of the leaves is consumed and only leaf veins and insect frass are left. Severe pinworm attack can cause yield losses of up to 100%.
T. absoluta is thus considered as a limiting factor for tomato production in several Latin American countries, wherein it accounts for about 70% of the losses and it becomes an increasing concern in Europe.
Control of this pest currently requires heavy application of insecticides. However, the increase of resistance of this pinworm to insecticides is reported. Moreover, blanket spraying of insecticides is harmful to both man and the environment.
Therefore, enhanced resistance of commercial tomato against the pinworm by introducing antixenosis and/or antibiosis resistance traits, or enhanced tolerance, is increasingly appreciated by commercial growers. So far such resistance or tolerance in a commercial tomato has not been reported against the pinworm.
In this context, varietal resistance to T. absoluta in tomatoes may be an important component of pest management programs. Resistance to T. absoluta has been found in several wild tomato accessions, inter alia in S. pennellii (corresponding to L. pennellii) LA716, S. peruvianum NAV29 and NAV 115, S. habrochaites (also named L. hirsutum) var. glabratum PI 134418 and PI 134417, S. habrochaites (also named L. hirsutum) var. hirsutum PI 127826, and L. hirsutum f. typicum LA1777 (Ecole, 2001). Resistance in these species is thought to be largely mediated by allelochemicals with pest-deterrent activities, such as methyl-ketones in PI 134417 (Maluf et al. 1997), sesquiterpenes (zingiberene) in PI127826 (Azevedo et al. 2003), and acylsugars (acylglucoses, acylfructoses) in LA 716 (Resende et al. 2006; Maluf et al. 2010).
These accessions were used extensively to develop commercial lines of S. lycopersicum with good levels of pest-resistance, especially resistance to T. absoluta. Maluf et al. (2010a and 2010b) report three proprietary precommercial breeding lines with high leaf acylsugars contents, presenting resistance to the South American tomato pinworm T. absoluta. The lines are however not commercial S. lycopersicum. Moreover, the resistance level of these lines and hybrid combinations made with them is far less than the resistant parent. No commercial hybrid varieties have apparently been obtained up to now from these 3 lines.
A few QTL analyses carried out in the progeny of some interspecific crosses between resistant wild tomato accessions and S. lycopersicum are also reported in the literature (Momotaz et al., 2010). They mainly emphasized the complexity of the resistance traits.
Therefore, in spite of intensive work in this respect and the importance of tomato production in the world, currently no tomato cultivars resistant to pinworm have been obtained though introgression of the trait from a wild tomato accession.
The difficulties encountered by breeders trying to develop commercial varieties from the wild tomato accessions have been so far explained by complex resistance traits, undesirable linkages, or both, and they have hampered efforts to incorporate the pinworm resistance to L. esculentum breeding lines and cultivars (see Eigenbrode et al., 1993).
In order to circumvent these difficulties, some authors have proposed as an alternative to use genetic resources of cultivated S. lycopersicum maintained in the germplasm banks. It was indeed hypothesized that the absence of known cultivated tomato variety resistant to T. absoluta could be associated with reduced genetic variability introduced during tomato domestication, leading to the loss of genes that control the production of allelochemicals involved in plant defenses. Recovery of this lost genetic variability was thus expected to improve plant resistance to pests and diseases (Oliveira et al., 2009). From this study, only two out of 57 accessions appear to present an allegedly promising resistance. The transfer of resistance factors from these accessions to commercial tomato has however not been carried out and no resistant commercial cultivar obtained to date.
There is thus an important need in the art to identify a reliable source of resistance or tolerance, which could be used to obtain resistant or tolerant commercial plants, and a need for improved commercial S. lycopersicum plants that are resistant to T. absoluta infestation.
The present invention provides commercial S. lycopersicum plants that display important tolerance or resistance to T. absoluta infestation, as well as methods that produce or identify S. lycopersicum plants or populations (germplasm) that display resistance to T. absoluta infestation. The present invention also discloses molecular genetic markers, especially SNPs, linked to the resistance loci.